This invention relates to a data storage device for storing digital data on a storage medium.
In a data storage device for converting analog signals such as audio signals and video signals to digital data and storing them on a storage medium, the data amount to be stored on the storage medium depends on the number of quantified bits and/or sampling frequencies of sample data.
Setting higher number of quantified bits or higher sampling frequency of the sample data allows high quality audio signals or video signals to be reproduced. However, in order to transmit the data in a short period of time it is necessary to use a data transmission path with a higher transfer speed. On the other hand, storing sample data by setting quantified bit numbers and sampling frequencies lower, data can be transmitted in a short period of time even by using a data transmission path with a lower transfer speed. However, it deteriorates the quality of reproducible audio signals or video signals.
In case where analog signals such as audio signals and video signals are converted to digital data and stored on a storage medium, when the analog signals to be stored can be obtained only once, they are often stored on the storage medium with higher quality.
However, when data stored on a storage medium is read out and transmitted to another device by using some communication device, the data transmission takes a long time if the communication device is an analog telephone line with a lower communication speed, for example. On the other hand, if the data transmitted through the telephone line, for example, is used as a news script in a broadcast station, for example, audio signals or video signals to be reproduced from the data only need to have quality enough for completing a task for creating a text script.
Further, when data stored on a storage medium is edited, a digital signal processor, DSP, for performing rapid computing has to be used in order to perform signal processing on a large amount of sample data by setting the quantified bit number and/or sampling frequency of sample data higher.
The present invention was made in view of those factors. It is an object of the present invention to provide a data storage device, which can store data reproducible of high quality and store data usable in a data transmission path with a lower transfer speed.
In order to overcome the above problem, according to a first aspect of the present invention there is provided a data storage device for converting analog signals to digital data and storing the digital data on a storage medium including a sampling unit for sampling the analog signals based on a sampling frequency, a compression unit for compressing the sample data output sequentially from the sampling data, a storage unit for storing compressed data output sequentially from the compression unit and a control unit for controlling the compression unit and the storage unit so as to divide sample data output sequentially from the sampling unit into a plurality of groups for every predetermined output period (interval), compress those group at different compression rates and store them in different storage areas, respectively.
According to a second aspect of the present invention there is provided a data storage device for converting analog signals to digital data and storing the digital data on a storage medium including a sampling unit for sampling the analog signals based on a sampling frequency, a storage unit for storing sample data output sequentially from the sampling unit and a control unit for controlling the storage unit so as to divide sample data output sequentially from the sampling unit into a plurality of groups for every predetermined output period (interval) and store them in different storage areas, respectively.
Here, different storage areas may be provided on a same storage medium or on different storage media.